Have you ever heard someone say something is
astronomical? If you want to say something is big,
you can say astronomical because things in space are so big.

The Sun is 93 million miles away, that is a big
number. Big numbers are hard to use.

What if we said the Sun was 520,800 million feet away?

Is that correct?

Yes it is, but if we use feet instead of miles the
number is much bigger and it is even harder to use. It is much
easier for scientists to do math with small numbers like 93 million
rather than large numbers like 520,800 million.

When we start to talk about stars the numbers get, well, astronomical. The nearest star is about 24 trillion
miles away. That is 24,000,000,000,000 miles. If a
scientist wanted to do a math problem with that huge number it would
be very difficult.

To make this number smaller we use something called
light years. Just like using miles instead of feet makes the
number above smaller, using light years instead of miles makes
numbers smaller. A light year means 6 trillion miles (6,000,000,000,000).

Can you remember that? A light year means 6
trillion miles.

Why do we call it a light year?

In one year light can travel 6 trillion miles.
Think about that for a moment. If you go outside tonight and
shine a flash light at the sky, in the next one year that light
will travel 6 trillion miles.

Assignment # 2.

Answer the following questions:

If the nearest star is 4 light years away how
many miles away is it?

How long will it take for the light from that star
to travel to the Earth?